The question arises all the time concerning which capacitor type to use for a particular
application. This table provides a guideline for starters, but is in no way exhaustive. (DA
= dielectric absorption)
The unofficial temperature coefficient designations for the capacitors are as follows:
The temperature coefficient is given as "P" for positive, "N" for negative, followed by a
3-digit value of the temperature coefficient in ppm/°C. For example "N220", is -200 ppm/°C,
and "P100" is +100 ppm/°C. The one exception in this system is "NPO" where an "O" instead
of "0" is used, but quite a number of people use "NP0." In any event "NPO" means stable with
temperature.
NPO Ceramic
(COG) |
<0.1% |
Tight tolerance
High Q factor, low K
Small case size
Inexpensive
Good stability
Wide range of values
Low inductance |
DA generally low, but may not be specified
Limited to small values (10 nF) |
Low loss, timing and tuning applications |
Monolithic
Ceramic
(High K) |
>0.2% |
Low inductance
Wide range of values |
Poor stability
Poor DA
High voltage coefficient |
|
X7R (BX)
(Barium Titanate) |
|
Inexpensive
Low DA available
Wide range of values
Smaller case size |
Damaged by temperature
>+85° C
Loose tolerances
High inductance |
Bypassing, coupling, and frequency discrimination circuits |
| Z5U & Y5V |
|
Smallest case size
Very large values |
Damaged by voltages
>25 WVDC
Very loose tolerances |
Bypassing and coupling |
| Polystyrene |
0.001%
to 0.02% |
Inexpensive
Low DA available
Wide range of values
Good stability |
Damaged by temperature
>+85° C
Large case size
High inductance |
Timers and filters |
| Polypropylene |
0.001%
to 0.02% |
Inexpensive
Low DA available
High dielectric strength
Wide range of values
Negative TC |
Damaged by temperature
>+105° C
Large case size
High inductance |
Stable oscillators and filters, sample and hold circuits and pulse handling circuits |
| Teflon |
0.003%
to 0.02% |
Low DA available
Excellent stability
Operational >+125° C
Wide range of values |
Relatively expensive
Large size
High inductance |
Timing and pulse shaping circuits |
| MOS |
0.01% |
Good DA
Small
Operational above +125° C
Low inductance |
Limited availability
Available only in small capacitance values |
|
| Polycarbonate |
0.1% |
Good long-term stability
Low cost
Wide temperature range |
Large size
DA limits to 8-bit applications
High inductance |
Timers, filters and applications in high ambient temperature |
| Polyester |
0.3%
to 0.5% |
Moderate stability
Low cost
Wide temperature range
Low inductance (stacked film)
Self-healing |
Large size
DA limits to 8-bit applications
High inductance |
Bypassing and coupling |
| Mica |
>0.003% |
Low loss at HF
Low inductance
Very stable
Available in 1% values or better |
Quite large
Low values (<10 nF)
Expensive |
|
| Aluminum Electrolytic |
High |
Large values
High currents
High voltages
Small size |
High leakage
Usually polarized
Poor stability
Poor accuracy
Inductive |
|
| Tantalum Electrolytic |
High |
Small size
Large values
Medium inductance
High melting point
High dielectric
strength
Good ductility |
Quite high leakage
Usually polarized
Expensive
Poor stability
Poor accuracy |
|
